Exogenous salicylic acid mediated herbicide (Paraquat) resistance in cyanobacterial biofertilizer Microchaete sp. NCCU-342.

Paddy field farming remains the dominant form of growing rice in modern times as the rice is the staple food for over half the world's population and is closely associated with food security and political stability of many countries. Record increase in rice production have been observed since the start of the Green Revolution. India is one of the largest paddy producer and exporter in the world. However, constant use of chemical herbicide like paraquat had shown adverse impact on the rice yield. Non-target organisms of the habitat including cyanobacterial paddy biofertilizer face the herbicide toxicity and are unable to perform efficiently their role as biofertilizer. Therefore, in the present study, an attempt has been made to enhance the paraquat resistance in rice biofertilizer (Microchaete sp. NCCU-342) by exogenous addition of salicylic acid. Paraquat showed toxicity in Microchaete sp. NCCU-342 in a dose-dependent manner. Concentration of paraquat >1.0 µM exhibited lethal effect since the beginning. Through successive narrow range experiment, LD50 value of paraquat was obtained as 0.6 µM. Biomass exposed to paraquat (LD50 value) and salicylic acid (0.3 mM) showed mitigation in free radical production (2.20 % MDA and 1.69 % H2O2) and enhancement in the activity of the antioxidant enzymes activity, i.e. SOD, CAT, APX (137.76 %, 87.45 %, 118 %, respectively) and osmolytes (3.8 % proline and 21.51% sucrose). Thus, for sustainable agricultural practice, especially for paddy field cyanobacterial biofertilizer, application of salicylic acid or organism with higher salicylic acid production ability may be an alternative to overcome the paraquat toxicity.

Weed seed bank dynamics responses to long-term chemical control in a rice-wheat cropping system.

BACKGROUND: It remains an open question if the long-term application of single chemical herbicides would inevitably lead to increased weed populations and result in out-of-control weeds. The annual dynamics of weed seed bank responses to different weeding measures (chemical herbicide, hand weeding and no weeding) in rice-wheat cropping systems were compared to observe the succession of weed communities under different weed selection pressures for 17 years. RESULTS: In unweeded rice-wheat cropping plots, the initially dominant broadleaf weeds were overtaken by grasses and eventually by sedges, while in plots subjected to chemical herbicide or hand weeding, broadleaf weeds remained dominant followed by grasses. The rice-wheat cropping system favoured the spread of paddy weed species; weeding had little effect on the composition of the dominant rice weeds but greatly influenced that of wheat weeds. Total seed density tended to decrease in both weeded and unweeded plots, but the species density and composition of the seed banks differed among plots treated differently. Weeding slightly increased weed species diversity and decreased weed community evenness and dominance in the first several years, but this scenario could have negative consequences in the long term; however, without weeding, stronger interspecific competition led to a decrease in weed species diversity whereas weed community evenness and dominance increased. CONCLUSION: Long-term and repeated application of pre-emergence chemical herbicides and hand weeding had similar effects on the weed community dynamics, indicating that exclusive application of pre-emergence herbicide could maintain the weed community at a durable relatively low infestation level. © 2019 Society of Chemical Industry.

Reducing environmental pollution by chemical herbicides using natural plant derivatives - allelopathy effect.

INTRODUCTION: Weeds are an important factor in determining production in the agricultural sector. Currently, weeds have been managed by employing synthetic weedicides chemicals. These chemicals have a negative impact on the environment through accumulation in soil and water, in addition to their effect on biological diversity. MATERIAL AND METHODS: A study was undertaken to evaluate the activity of the aqueous extract of leaves from; Nerium (Nerium oleander L), olives (Olea europaea L) and castor (Ricinus communis L) on the control of Cyperus rotundus L. The study comprised of two components: three plant species, and the uses of three planta extracts concentration (5%, 7.5% and 10%) and their impact on germination and inhibition of seedling growth. RESULTS: The results from using Nerium extract in comparison with Tibenuron and the two other plants extracts gave 90% inhibition at concentrations of 5% and 10%, while the concentration of 2.5% gave the lowest inhibition rates for germination of all plant extracts under study. The second experiment carried out using 10% concentration of the Nerium extract gave complete inhibition (100%), compared with the same concentrations of other plants extract and weedicides. CONCLUSIONS: The current study indicates the possibility of using natural products of plant origin as alternatives to chemical herbicides as one of the means of biological control to reducing environment pollution.